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This article provides a novel theoretical model and extensive empirical evidence to explain the decline of a historically important patent law doctrine known as the “doctrine of equivalents.” In recent years, distinguished academics have studied the doctrine of equivalents. While these scholars noted that the doctrine of equivalents had decreased in its successful use and provided some grounds for the decline, none clearly explained why. As such, the cause and precise mechanism behind the so-called “demise” of the doctrine of equivalents have largely remained a mystery.

This article explains that the demise occurred because of two complementary forces discussed for the first time in this article: “doctrinal reallocation” and “doctrinal displacement.” Under doctrinal reallocation, a substantive doctrine may become more important after a shift in adjudicative control over that doctrine, for example, through reallocation of the decision-making authority from a jury to a judge. Doctrinal displacement posits that an increase in the importance of a doctrine may in turn decrease the importance of another, typically related, doctrine. This article’s empirical results support the position that the demise of the doctrine of equivalents was a result of these twin forces.